The search for new therapeutic agents has been greatly aided in recent years by better understanding of the structure of proteins and other biomolecules associated with target diseases. One important class of these proteins is the sigma (σ) receptor, a cell surface receptor of the central nervous system (CNS) which may be related to the dysphoric, hallucinogenic and cardiac stimulant effects of opioids. From studies of the biology and function of sigma receptors, evidence has been presented that sigma receptor ligands may be useful in the treatment of psychosis and movement disorders such as dystonia and tardive dyskinesia, and motor disturbances associated with Huntington's chorea or Tourette's syndrome and in Parkinson's disease (Walker, J. M. et al, Pharmacological Reviews, 1990, 42, 355). It has been reported that the known sigma receptor ligand rimcazole clinically shows effects in the treatment of psychosis (Snyder, S. H., Largent, B. L. J. Neuropsychiatry 1989, 1, 7). The sigma binding sites have preferential affinity for the dextrorotatory isomers of certain opiate benzomorphans, such as (+)-SKF 10047, (+)-cyclazocine, and (+)-pentazocine and also for some narcoleptics such as haloperidol.
The sigma receptor has at least two subtypes, which may be discriminated by stereoselective isomers of these pharmacoactive drugs. SKF 10047 has nanomolar affinity for the sigma-1 (σ1) receptor and has micromolar affinity for the sigma-2 (σ2) isoform. Haloperidol has similar affinities for both subtypes. Endogenous sigma ligands are not known, although progesterone has been suggested to be one of them. Possible sigma-site-mediated drug effects include modulation of glutamate receptor function, neurotransmitter response, neuroprotection, behavior, and cognition (Quirion, R. et al. Trends Pharmacol. Sci., 1992, 13:85-86). Most studies have implied that sigma binding sites (receptors) are plasmalemmal elements of the signal transduction cascade. Drugs reported to be selective sigma ligands have been evaluated as antipsychotics (Hanner, M. et al. Proc. Natl. Acad. Sci., 1996, 93:8072-8077). The existence of sigma receptors in the CNS, immune and endocrine systems have suggested a likelihood that it may serve as link between the three systems.
In view of the potential therapeutic applications of agonists or antagonists of the sigma receptor, a great effort has been directed to find selective ligands. Thus, the prior art discloses different sigma receptor ligands. 1-(4-(2-((1-(3,4-difluorophenyl)-1H-pyrazol-3-yl)methoxy)ethyl)piperazin-1-yl)ethanone is one of such promising sigma receptor ligands. The compound and its synthesis are disclosed and claimed in WO 2011/147910.
1-(4-(2-((1-(3,4-Difluorophenyl)-1H-pyrazol-3-yl)methoxy)ethyl)piperazin-1-yl)ethanone is a highly selective sigma-1 (σ1) receptor antagonist. It displays strong analgesic activity in the treatment and prevention of chronic and acute pain, and particularly, neuropathic pain. The compound has a molecular weight of 364.39 Da and a pKa of 6.37. The structural formula of the compound is:

To carry out its pharmaceutical development and realize its potential, there is a need in the art for additional forms of 1-(4-(2-((1-(3,4-difluorophenyl)-1H-pyrazol-3-yl)methoxy)ethyl)piperazin-1-yl)ethanone that will facilitate the preparation of better formulations of this active pharmaceutical ingredient.
In this regard, alternative forms of the compound may have widely different properties such as, for example, enhanced thermodynamic stability, higher purity or improved bioavailability (e.g. better absorption, dissolution patterns). Specific compound forms could also facilitate the manufacturing (e.g. enhanced flowability), handling and storage (e.g. non-hygroscopic, long shelf life) of the compound formulations or allow the use of a lower dose of the therapeutic agent, thus decreasing its potential side effects. Thus, it is important to provide such forms, having improved properties for pharmaceutical use.